1. Field of the Invention:
The present invention relates to the preparation of decorative and/or protective coatings for substrates. More specifically, the invention relates to the use of metal salt in the prevention or reduction of color shift in metal decorating inks.
2. Brief Description of the Prior Art:
The use of metal salts in coating compositions is generally known in the art. In the main, the art has disclosed the use of metal salts as driers. The art has also disclosed the use of metal salts as corrosion inhibitors and adhesion promoters. In a seemingly unrelated field, the art has disclosed the use of metal salts in prevention of cyan dye fading in color-developed prints and films. However, in the field of coatings, the art has not disclosed the use of metal salts in preventing or reducing color shift in, say, can decorating inks.
Decorative can coatings can be prepared by printing ink labels of single or multiple color prints directly on substrates or indirectly on substrates coated with base-coatings. The printed ink labels can be topcoated with clear coatings. It has been found that when water-reducible coating compositions are used in top-coating the printed inks in a wet-on-wet mode, there results a change in hue in certain organic pigments or dyes of the inks. The change in hue is described herein as a color shift in the ink. The change in hue is either tolerated or compensated for by producing higher than the desired color strength with rather expensive pigments. The higher color strength shifts to the desired color strength when top-coated with water-reducible compositions.
By the present invention, it has been found that addition of metal compounds such as metal salts to water-reducible compositions effects reduction or prevention of color shift in inks.